In his first-ever interview, the sole Australian survivor of the Waco siege has revealed to 60 Minutes what really took place during the 51-day stand-off, and why he believes crazed cult leader David Koresh will one day return to Earth as the son of God.

An autopsy carried out on Ms Steele's body was unable to determine a cause of death.

Insp Marsh said that wasn't unusual, given the body was not found for five days, but it was clear from other evidence it was a murder.

The drug squad was originally brought in to investigate whether there was a connection with Ms Steele's death, but no dangerous drugs were found at the crime scenes or on anyone interviewed.

Ms Steele was farewelled by her husband and two boys at a private funeral service on Thursday.

Insp Marsh said it was a difficult time for the family, but he understood the trio would return to Cooktown.

All of the evidence has been sent to Brisbane and Cairns for analysis, while investigators on the ground were continuing the "painstaking process" of sifting through CCTV and cross-referencing witness statements.

He said police were confident the crime would be solved.

"A lot of pressure obviously will be on the person or persons who have committed this crime," he said.

"If not now, it will soon become apparent who has done it and they will be reported to the police."